Document that io.isdir & io.isfile may throw

Author: Sainan

docs/Runtime Environment/IO.md

@@ -38,6 +38,8 @@ print(io.part("/path/to/foo.txt", "name")) -- "foo.txt"
 1. A string path or file stream.
 #### Returns
 A boolean indicating if the path led toward a directory.
+#### Errors
+Raises a Lua error if the given path didn't lead to anything.
 ```pluto
 local path = "./dir/main/"
 local bool = io.isdir(path)
@@ -53,6 +55,8 @@ end
 1. A string path or file stream.
 #### Returns
 A boolean indicating if the path led towards a file.
+#### Errors
+Raises a Lua error if the given path didn't lead to anything.
 ```pluto
 local path = "./isfile/file"
 local bool = io.isfile(path)